The preparation and characterization of dimers and polymers wherein two or more cages are directly linked, represents an important frontier in the chemistry of fullerene derivatives. We have prepared novel oxo- and methylene bridged C60 dimers, the first well-characterized compounds containing fullerene-fullerene bonds. We are currently exploring the scope of the thermolytic transformations of oxo- and methanofullerenes and studying the chemical and physical properties of the novel adducts 3 and 4. Additions of 1 and 2 to simple alkenes would provide invaluable mechanistic insights as well as synthetic access to new families of fullerene derivatives. A paper describing this work appeared in J. Am. Chem. Soc. 117 (1995) 9359. This project provided the impetus for us to improve our ability to measure negative ions by electrospray ionization mass spectrometry and investigate the use of electron transfer reagents in solution. We have continued this investigation and plan to determine whether ionization by electron transfer is of use for examining certain classes of biologically important compounds such as metalloporphyrins.